The present invention relates to a hydrauliuc damper for a vehicular suspension system.
Japanese Utility Model Application First (unexamined) Publication No. 60-2035 discloses a hydraulic damper. This known hydraulic damper comprises a cylinder containing a hydraulic fluid, a piston within the cylinder and mounted on a piston rod. The piston has one or more rebound valve passages having one ends communicating with a first chamber adjacent to an upper face of the piston and opposite ends opening at an annular groove contained in a lower face of the piston. The piston has one or more compression valve passages having one ends opening to a second chamber adjacent to the lower face of the piston and opposite ends opening at an annular groove contained in the upper face of the piston. A valve disc is mounted on the upper face to bridge a peripheral annular groove created by the adjacent annular groove. Another valve disc is mounted on the lower face of the piston to bridge a peripheral annular groove created by the adjacent annular groove. The piston rod includes a valve sleeve formed with a plurality of ports communicating with the first chamber. Rotatably disposed in the valve sleeve is a valve element having a passage having one end closed and an opposite end communicating with the first chamber. The valve element has openings mating with the plurality of ports. The mating ports and openings cooperate with each other to variably restrict bypass flow of hydraulic fluid between the first and second chambers.
U.S. Pat. No. 4,615,420 discloses a hydraulic damper. This known hydraulic damper includes a first set of one or more passages controlled by two valve mechanisms, which conduct fluid only during rebound stroke. A second set of passages, controlled by a single valve mechanism, conducts fluid during all compression and rebound strokes. A third set of passages uncontrolled by any valve mechanism conducts fluid during all compression and rebound strokes.
An object of the present invention is to provide a hydraulic damper of the type including a valve element within a valve sleeve wherein a sufficiently wide range of damping force vs. piston stroke characteristics is provided.